Calmodulin Localization and its Effects on Endocytic and Phagocytic Membrane Trafficking in Paramecium multimicronucleatum

Abstract

In ciliates, calmodulin (CaM), as in other cells, has multiple functions, such as activation of regulatory enzymes and modulating calcium-dependent cellular processes. By immunogold localization, CaM is concentrated at multiple sites in Paramecium. It is seen scattered over the cytosol, but bound to its matrix, and is concentrated at the pores of the contractile vacuole complexes and with at least three microtubular arrays. It was localized peripheral to the nine-doublet microtubules of the ciliary axonemes. The most striking localization was on the akinetic side only of the cytopharyngeal microtubular ribbons opposite the side where the discoidal vesicles, acidosomes and the 100-nm carrier vesicles bind and move. CaM was also present at the periphery of the postoral microtubular bundles along which the early vacuole moves and was associated with the cytoproct microtubules that guide the spent digestive vacuoles to the cytoproct. It was not found on the membranes of, or in the interior of nuclei, mitochondria, phagosomes, and trichocysts, and was only sparsely scattered over the cytosolic sides of discoidal vesicles, acidosomes, lysosomes, and digestive vacuoles. Together the associations with specific microtubular arrays and the effects of trifluoperazine and calmidazolium indicate that CaM is involved (i) in vesicle transport to the cytopharynx area for vacuole formation and subsequent vacuole acidification, (ii) in early vacuole transport along the postoral fiber, and (iii) in transporting the spent vacuole to the cytoproct. Higher CaM concentrations subjacent to the cell's pellicle and close to the decorated tubules of the contractile vacuole complex may support a role for CaM in ion traffic.

Identification of Contractile Vacuole Proteins in Trypanosoma cruzi

“…VAMP1 is included because of its similarity (2.8e −12 ) with PtSyb2-2, a Paramecium tetraurelia synaptobrevin that localizes to the contractile vacuole [21]. Calmodulin is included in Table 1 because it was shown to be localized in the CV of T. cruzi by immunofluorescence analysis using human antibodies [5] and is present in the CV of D. discoideum [22] and Paramecium multimicronucleatum [23]. A homologue to a vacuolar phosphate transporter from yeast (Pho91) [24] annotated as a sodium/sulphate symporter is also included because orthophosphate (Pi) was shown to be abundant in the CV of T. cruzi [4].…”

Molecular aspects of calcium signalling at the crossroads of unikont and bikont eukaryote evolution – The ciliated protozoan Paramecium in focus

“…Calmodulin (CaM) is enriched at several sites of the Paramecium cell [75,76]: along the cell membrane, in cilia and on vesicles of the food vacuole (phagolysosome) system as well as along the contractile vacuole and its extensions [75]. Here, CaM is associated with microtubules [76], so one can expects a stabilizing effect [77].…”

“…Here, CaM is associated with microtubules [76], so one can expects a stabilizing effect [77]. At the cell membrane CaM activates Ca 2+ /CaM-activated cation influx channels (Section 6.1) and the PMCA has a CaM binding domain for its activation [50] (although CaM binding still remains to be ascertained with Paramecium).…”

New Insights into Roles of Acidocalcisomes and Contractile Vacuole Complex in Osmoregulation in Protists

“…The presence of several proteins related to Ca 2+ signaling underscores the role of the CVC in this process (see below): a Ca 2+ -ATPase (PAT1) in D. discoideum (Marchesini et al, 2002; Moniakis et al, 1999), an IP 3 R in Paramecium tetraurelia (Ladenburger et al, 2006), the Ca 2+ binding proteins calmodulin (CaM) (Zhu and Clarke, 1992; Zhu et al, 1993) and copine A (Damer et al, 2007) in D. discoideum , and also CaM in P. multimicronucleatum (Fok et al, 2008) and T. cruzi (Ulrich et al, 2011), and the P2X receptors in D. discoideum (Fountain et al, 2007; Ludlow et al, 2009; Sivaramakrishnan and Fountain, 2012a, b). These receptors are Ca 2+ permeable ligand-gated ion channels activated by ATP.…”